have you looked into inappropriate sinus tachycardia? it falls under the pots 'umbrella' & this sounds like it for sure.

Happens to me. Not sure what to actually do but what helps me is distracting myself until it passes so I don’t stress my body more by being concerned. Wait it out and try to investigate when I’m not in the middle of it. It’s scary and very uncomfortable but I don’t have anything other than try to help it pass as quickly as I can. Usually happens more open when neck and upper body is tight and haven’t been exercising consistently.

I have these same moments with my POTS and it's really scary sometimes. My strategy is I try to distract myself with music, grounding, and deep breathing until my body can better adjust. This doesn't work all the time but it can usually tide me over until I can get to a safe place. Sending positive thoughts:)